Roughening of SU8 Waveguides to Accentuate Light Scattering

In this study, we investigate a technique for roughening the surface of multi-mode-interference (MMI) waveguides so that interference modes can be more easily imaged. The MMIs are constructed on silicon substates using SU8, a photodefineable polymer that has low absorption of visible light and a refractive index of 1.59. We find that exposing the SU8 to an O
2
plasma in a reactive ion etcher creates a surface layer of nanoscopic grass which is efficient at scattering light.